This invention relates to bifold door closures which are counterbalanced in weight and will remain open at any given position. More specifically, this invention relates to bifold door closures which occupy a minimum of space when in the fully open position and which are counterbalanced in weight so as to remain open in any given position and which may be opened without the use of tracks, springs, levers or other complicated mechanisms. Furthermore, this invention is related to a bifold closure which, when opened, will not sag or bind thereby allowing a complete bifolding of one section over another.
Door closures of various types, especially for large openings, are well known in the art, but all have their attending disadvantages. For example, closures used in airplane hangars, warehouses, garages and the like often raise overhead by means of a tracking system and are heavy and cumbersome to operate and/or require a torsion spring, counterweight or other mechanism to offset the weight of the door while being raised. Moreover, these doors occupy considerable space, often swing with a large arc or radius, and are not, in general, capable of being opened and balanced at any given position. These doors also usually open inwardly. Some doors are sectionalized so that, by a system of rollers on a track, they can be angled around a 90.degree. curve in the tracking system. The mechanism for opening and closing these doors is such that the door is not balanced in any given position, and hence, will usually close by its own weight when brought to a certain partially closed position.
Another typical type of closure for large doors is a solid structure wherein the bottom swings outwardly and upwardly and the top swings backwardly in an arcuate pattern. These doors are heavy and when left open there is nothing to offset their weight and so have a tendency to easily sag and warp.
Other types of closures are known such as horizontally opening doors of either an accordian type or doors which either swing inwardly or outwardly or are bifold in equal sections. Such horizontally opening doors usually require considerable space thereby lessening the width of the opening that can be utilized for ingress or egress.